1. Field of the Invention
The present invention relates to a vehicle lamp having a reflecting member in a lamp compartment.
2. Related Art
As reflectors used for vehicle lamps such as headlamps which require high luminous intensity and extension reflectors which are disposed as decorative members in such a manner as to surround reflectors, there are known reflectors and extension reflectors in which a reflecting surface is made up of an aluminum deposited coat by applying an aluminum vapor deposition treatment to a surface of a synthetic resin base. In addition, since a high constant regular reflectivity of about 90% can be obtained on the aluminum deposited reflecting surface, such aluminum deposited reflecting surfaces are widely used not only for headlamps but also for other vehicle lamps.
However, there still exists a loss in regular reflectivity of on the order of 10% on the aluminum deposited reflecting surface, and hence there has been a demand for a further improvement in regular reflectivity.
Then, on the advent of development of a silver deposited coat having a high regular reflectivity (99%) for use for reflecting surfaces of indoor illumination appliances, a study was started on the application of the developed silver deposited coat to reflecting surfaces of reflecting members of vehicle lamps. However, the silver deposited coat reacts (generates silver oxide and silver sulfide) when contacting water, oxygen (heated oxygen) and sulfur dioxide gas (sweat, exhaust emissions) in the atmosphere to thereby be easily discolored (yellowed) and corroded, leading to a remarkable reduction in regular reflectivity.
Then, proposed in JP-A-2000-106017 (see FIG. 9) is a top coat layer 3 and an under coat layer 4, which are made of a modified silicone resin having superior gas barrier properties under high temperatures, and formed to be superposed on a silver deposited coat 2 formed on a surface of a synthetic resin base 1, so that the top coat layer 3 and the under coat layer 4 function as gas barriers against water, oxygen (heated oxygen) and sulfur dioxide gas (sweat, exhaust emissions) which are contained in the atmosphere so as to suppress the discoloration and corrosion of the silver deposited coat 2, the high regular reflectivity being thereby maintained.
In the reflector of JP-A-2000-106017 which utilizes the gas barrier properties of the top coat layer and the under coat layer which are made of the modified silicone resin, however, while the top coat layer and the under coat layer are effective to a certain extent in suppressing the discoloration (yellow discoloration) of the silver deposited reflecting surface (the silver deposited coat), there was caused a problem that discoloration and corrosion occur after many hours have elapsed (a heat resistance test of 400 hours), thereby reducing the regular reflectivity.
A study carried out by the inventor disclosed a fact that the cause for the discoloration (yellow discoloration) was attributed not only to the contact of the gases (moisture, oxygen and sulfur dioxide gas) in the atmosphere with Ag atoms but also to the agglomeration of Ag atoms making up the silver deposited coat as a result of vibration (migration) of the Ag atoms by thermal energy.
Namely, as shown in FIG. 10, when subjected to thermal energy, Ag atoms (crystalline particles of Ag) constituting the silver deposited coat formed on the surface of the base vibrate relatively from an original state in which they are arranged in a proper fashion and agglomerate together at certain locations to thereby form fine irregularities on the surface of the silver deposited coat. Then, since light (blue) with a short wave range is absorbed and light (yellow to red) with a long wave range is reflected on areas where such fine irregularities are formed, the whole of silver deposited coat looks yellow.